1. Field of the Invention
The present invention relates to a heat development apparatus for recording an image on a dry recording material, and more particularly to a structure of a cooling section for cooling a recording material heated by a heat development section for subjecting to a heat treatment, the recording material on which a latent image has been formed.
2. Description of the Related Art
An image recording apparatus or recording a medical image for use in a digital radiography system, a CT, an MR or the like which uses a heat accumulating fluorescent sheet is known. The foregoing apparatus employs a wet system for obtaining a reproduced image by performing a wet process after an image has been photographed or recorded on a silver-salt photographic photosensitive material.
In recent years, a recording apparatus has attracted attention which employs a dry system in which the wet process is not performed. The foregoing recording apparatus is arranged to use a photosensitive and/or thermo-sensitive recording material or a film made of a heat development photosensitive material (hereinafter called "recording materials"). In the recording apparatus using the dry system, the recording material is irradiated (scanned) with a laser beam in an exposing section so that a latent image is formed. Then, the recording material is, in a heat development section, brought into contact with a heating means so that heat development is performed. Then, the recording material on which an image has been formed is discharged to the outside of the apparatus.
The dry system of the foregoing type is able to form an image in a shorter time as compared with the wet process. Moreover, the problem of a necessity of disposal of waste liquid produced in the wet process can be overcome. Therefore, increase in the demand of the dry system is expected.
FIG. 1 shows a conventional heat development apparatus. A cooling section 400 indicated with a dashed line in a heat development apparatus 10 is a portion added according to the present invention.
Referring to FIG. 1, the image forming apparatus 10 is an apparatus arranged to use a heat development photosensitive material (hereinafter called a "recording material A") which does not require the wet development process. Moreover, scanning exposure using laser beam L is performed to expose the recording material A to correspond to a required image so that a latent image is formed. Then, heat development is performed so that a visible image is obtained. The image forming apparatus 10 comprises a recording-material supply section 12, a width aligning section 14, an image exposing section 16 and a heat development section 18 disposed in this order in a direction in which the recording material A is conveyed.
The recording-material supply section 12 has two sections 80 having inside portions 22 and 24 to permit selective use of the recording materials A (for example, B4-size recording materials or half-cut recording materials) set in the foregoing sections through magazines 100. The recording material A is a recording material on which an image is recorded (exposed) by the laser beam L and which is developed with heat to develop color. In accordance with a print command, an uppermost recording material A in the magazine 100 selected by suction cups 26 and 28 structured to suck each sheet in a state in which the cover of the magazine is opened is taken out. Then, the recording material A is guided by paired supply rollers 30 and 32, paired conveying rollers 34 and 36 and conveying guides 38, 40 and 42 disposed downstream in the conveying direction so as to be conveyed to the width aligning section 14.
The width aligning section 14 aligns the position of the recording material A with a direction (hereinafter called a "widthwise direction") perpendicular to the conveying direction. In the downstream image exposing section 16, the width aligning section 14 performs alignment of the recording material A in the main scanning direction, that is, so-called side regist. Then, a conveying roller pair 44 conveys the recording material A to the downstream image exposing section 16.
The downstream image exposing section 16 uses a laser beam to expose the recording material A to correspond to the image the image exposing section 16 incorporating an exposing unit 46 and a sub-scan conveying means 48.
FIG. 2 shows an example of the image exposing section 16.
Referring to FIG. 2, the image exposing section 16 incorporates:
(1) a first laser-beam source 50 having a semiconductor laser 50a for emitting laser beam L0 having a wavelength serving as a reference for a recording operation, a collimater lens 50b for converting the laser beams into a parallel luminous flux and a cylindrical lens 50c; and
(2) a second laser-beam source 200 having a second semiconductor laser unit 200a for emitting laser beam L1 in a direction perpendicular to the direction of the optical axis of the first laser-beam source 50 and having a different wavelength from that of the first laser beam, a collimater leans 200b and a cylindrical lens 200c.
Light emitted from each of the laser-beam sources 50 and 200 is allowed to pass through a polarizing beam splitter 202 so as to be formed into superimposed beams having the same phase. Then, the beams are allowed to pass through a reflecting mirror 204 so as to be made incident on a polygonal mirror 54. When the polygonal mirror 54 is rotated, the laser beam is applied in a main scanning direction b through a f.theta. lens 56 and a cylindrical mirror 58 while the laser beam is being polarized.
In response to an input image signal, a control unit (not shown) operates a driver 52 so as to rotate a conveying motor 206 provided for a polygonal mirror (a rotative polygonal mirror) 54 and a roller pair 60,62. Thus, while the recording material A is being scanned in the main scanning direction b with the laser beam, the recording material A is conveyed in a sub-scanning direction a.
As a result, while the recording material A is being sequentially conveyed in the sub-scanning direction by the conveying motor 206 provided for the roller pair 60,62, a latent image having a predetermined outline is formed on the surface of the recording material A in the main scanning direction.
As described above, the first laser beam and the second laser beam, which is emitted in a direction perpendicular to the optical direction of the first laser beam and having a different wavelength are used. Thus, generation of interference fringes caused from reflection of the laser beam in the layer occurring owning to a thin thickness of an Em (emulsion) can be prevented. As a result, a latent image having a clear outline can be formed on the surface of the recording material A.
Referring again to FIG. 1, then, the recording material A caused to have the latent image formed by the image exposing section 16 shown in FIG. 2 is conveyed to the heat development section 18 by conveying roller pairs 64, 66 and 132. The heat development section 18 is a section for heating the recording material A to perform the heat development to convert the latent image into a visible image. A plate heater 320 accommodated in the heat development section 18 includes a heating member which is a plate-like heating member including a heating member, such as a nichrome wire, which is laid flatly. Thus, the development temperature for the recording material A is maintained. As shown in the drawing, the plate heater 320 projects upwards. Moreover, there are provided a supply roller 326 serving as a conveying means for relatively moving the recording material A with respect to the plate heater 320 while making, contact the recording material A with the surface of the plate heater 320; and a pressing roller 322 which transmits heat from the plate heater 320 to the recording material A and disposed adjacent to the lower surface oft the plate heater 320. Moreover, a heat insulating cover 325 for maintaining the temperature is disposed opposite to the plate heater 320 of the pressing roller 322.
As a result of the foregoing structure, the recording material A passes through a space between the pressing roller 322 and the plate heater 320 by dint of the conveying rotations of the supply roller 326. Then, the heat treatment is performed so that the recording material A is developed with heat. Then, the exposure process is performed so that the recorded latent image is converted into a visible image. Since the conveyance is performed such that the leading end is pressed against the plate heater 320, buckling of the recording material A can be prevented.
The recording material A discharged from the heat development section 18 is, by a conveying roller pair 140, guided to a guide plate 142. Then, the recording materials A are accumulated in a tray 146 from the discharge roller pair 144.
The heat development photosensitive material, which is the recording material A, incorporates a surface protective layer for protecting an image forming layer and preventing adhesion; the Em (emulsion) layer; a support-member layer (usually made of PET); and a back layer (and an AH (antihallation) layer in some cases).
The Em layer is an image forming layer formed on the surface of the support-member layer on which the laser beam L is made incident and which contains a binder composed of latex at a ratio of 50% or higher and a reducing agent which is organic silver salt. When the image forming, layer is exposed to incident laser beam L, a photocatalyst, such as photosensitive silver halide, forms a core for a latent image. When the core of the latent image is heated, the action of the reducing agent moves silver of the ionized organic silver salt so as to be bonded with the photosensitive silver halide and formed into crystal silver with which an image is formed. As the organic silver salt, silver salt of an organic acid, preferably silver salt of long-chain fatty carboxylic acid having 10 to 30 carbon atoms and organic or inorganic silver salt, the ligant of which has a stability factor coefficient of complex of 4.0 to 10.0 are exemplified. Specifically, the following materials are exemplified: silver salt of behenic acid, silver salt of arachidic acid, silver stearate, silver olerate, silver laurate, silver caproate, silver myristate. silver palmitate, silver maleate, silver fumarate, silver tartrate, silver linoleate, silver butyrate and silver camphorate. The image forming layer of the recording material contains a material, for example, photosensitive silver halide (hereinafter called "silver halide) which is converted into a photocatalyst after it has been exposed to light.
The image forming layer of the recording material or another layer on the same surface of the image forming layer may contain an additive which is known as a tone adjuster in a preferred quantity of 0.1 mol % to 50 mol % with respect to one mol of silver to raise the optical density. Note that the tone adjuster may be a precursor induced to have an effective function only when the development process is performed. The tone adjuster may be any one of a variety of known tone adjusters for use in the recording material. Specifically, the following materials are exemplified: a phthalimide compound, such as phthalimide or N-hydroyphthalimide; cyclic imide, such as succinimide, pyrazoline-5-on; naphthalic imide, such as N-hydroxy-1,8-naphthalic imide: cobalt complex, such as cobalt hexamine trifluoroacetate; mercaptan, such as 3-mercapto-1,2,4-triazole or 2,4-dimercaptopyrimidine; phthalazinone derivatie, such as 4-(1-naphtyl) phthalazinon; and its metal salt. The foregoing tone adjuster is added to the solution, which must be applied, as solution, powder or dispersed solid particles.
The sensitizing coloring matter must be capable of spectrosensitizing silver halide in a required wavelength region when the sensitizing coloring matter has been adsorbed to silver halide particles. To add the sensitizing color matter to the silver halide emulsion, it may directly be dispersed in the emulsion or it may be dissolved in single or a mixed solution of water, methanol, ethanol, N,N-dimethylformamide or the like, followed by adding the solution to the emulsion.
The surface protective layer is formed by an adhesion preventive material exemplified by wax, silica particles, elastomer-type block copolymer containing styrene (styrene-butadiene-styrene or the like), cellulose acetate, cellulose acetate butylate and cellulose propionate.
It is preferable that the antihallation (AH) layer is a layer, the maximum absorption of which is 0.3 to 2 in a required wavelength range and absorption of which is 0.001 to 0.5 in a visible region after the process has been completed. When the halation preventive dye is employed, any compound capable of satisfying the following requirement may be employed: the dye must be capable of performing required absorption in the wavelength and; the absorption must sufficiently be restrained in the visible region after the process has been completed; and a preferred absorbance spectrum shape for the antihalation layer can be obtained. Although the following materials are exemplified, the material is not limited to the following materials. As single dye, compounds disclosed in Japanese Patent Laid-Open No. 7-11432 and Japanese Patent Laid-Open No. 7-13295 are exemplified. As dyes which perform decoloration by carrying out processes, compounds disclosed in Japanese Patent Laid-Open No. 52-139136 and Japanese Patent Laid-Open No. 7-199409 are exemplified. It is preferable that the foregoing recording material has the image forming layer on either surface of the support member and a back layer on another surface.
To improve conveyance ease, a matting agent may be added to the back layer. In general, the matting agent is in the form of particles of organic or inorganic compound which is dissoluble in water. The preferred organic compound is exemplified by water dissoluble vinyl polymer, such as polymethylacrylate, methyl cellulose, carboxy starch and carboxy nitrophenyl starch. The preferred inorganic compound is exemplified by silicon dioxide, titanium dioxide, magnesium dioxide, aluminum oxide and barium sulfate.
The binder for forming the back layer may be any one of a variety of colorless, transparent or semitransparent resins. The resin is exemplified by gelatin, arabic rubber, polovinyl alcohol, hydroxyethyl cellulose, cellulose acetate, cellulose acetate butylate, casein, starch, poly (metha) acrylate, polymethylmethacrylate and polyvinyl chloride.
It is preferable that the back layer is a layer, the maximum absorption is 0.3 to 2 in a required wavelength range. If necessary, the halation preventive dye for use in the foregoing antihallation layer may be added to the back layer.
Since the recording, material A contains the various chemical substances, a variety of fat and oil components are vaporized from the recording material A with heat generated by the heat development section 18. The foregoing components adhere to the following roller or the like, causing another problem to arise in that an adverse influence is exerted on the roller or the like.
A portion of the foregoing dry systems has a structure that the recording material is conveyed while the recording material is being pressed against the side surface of the plate heater by the pressing roller or the like so as to perform the heat development. Since the plate heater is heated to a high level of 100.degree. C. or higher, also the recording material immediately after it has been subjected to the heat development is heated to a high level.
Therefore, when the recording material is naturally cooled, a long time is required for the recording material to be cooled. Moreover, the temperature in the apparatus changes the time required for the development operation to be interrupted. It leads to a fact that the developed image has a difference in the density (irregular density). Thus, a variety of problems have been raised.
To solve the foregoing problems, a variety of suggestions have been made. For example, an "improved heat development method" disclosed in Japanese Patent Laid-Open No. 3-208048 has a cooling step for cooling a photosensitive material subjected to the heat development.
However, only the cooling step is insufficient to form an image having a high quality free from irregular density. A fact has been found that uniform and stable cooling is required to form an image having a high quality.
Moreover, another fact has been found that inadequate cooling temperatures cause creases of the recording material to occur in a process from the heat development to the cooling step. In this case, flatness deteriorates. What is worse, a fat and oil component vaporizes when the recording material is heated. If the fat and oil component is not cleaned off the component adheres to the recording material and, therefore, the quality of the image deteriorates.